In recent years, in view of energy saving and environmental conservation, illumination apparatuses using light-emitting diodes (hereinafter also referred to as “LED”) as light sources, (such as LED bulbs), have been used in place of incandescent lamps. However, the conventional illumination apparatuses using LED as a light source emit light only forward, and cannot emit light in a wide range direction unlike incandescent lamps. Therefore, the conventional illumination apparatuses cannot extensively illuminate a room by using reflected light from the ceiling or the walls unlike incandescent lamps.
To bring the light distribution characteristics of the conventional illumination apparatus using an LED as a light source close to those of incandescent lamps, it is suggested to control the distribution of light emitted from the LED with a light flux controlling member (see, e.g., PTL 1). FIG. 1 is a sectional view of a main portion illustrating the configuration of an illumination apparatus disclosed in PTL 1. As illustrated in FIG. 1, illumination apparatus 10 includes a plurality of LEDs 12 disposed on a substrate, and cylindrical case 14 made of optically transparent material disposed around LEDs 12. The top surface of case 14 is formed to have an inverted truncated cone shape.
Aluminum plate 16 that reflects light is attached to the oblique surface of the truncated cone, and serves as a reflection surface. On the other hand, the planar surface of the truncated cone serves as transmission window 18 that transmits light. As indicated by arrows in FIG. 1, a part of light emitted from LEDs 12 passes through transmission window 18 to be emitted forward (upward direction). Further, a part of the light emitted from LED 12 is reflected by aluminum plate 16 to be emitted sideward (horizontal direction) and backward (downward direction).
The control of the traveling direction of light emitted from the LEDs using a light flux controlling member in this manner makes it possible to obtain emitted light not only forward, but also sideward and backward. Accordingly, the use of the light flux controlling member (reflection surface) disclosed in PTL 1 makes it possible to bring the light distribution characteristics of the illumination apparatus (LED bulb) close to those of incandescent lamps to a certain extent.